Aqueous uretdione group-containing compositions and method for producing same

ABSTRACT

The invention relates to aqueous uretdione group-containing compositions comprising or consisting of (A) at least one uretdione group-containing curing agent based on aliphatic, cycloaliphatic, aliphatic and/or aromatic polyisocyanates which do not contain chemically bonded hydrophilating groups; (B) at least one polyacrylate copolymer; (C) optionally solvents; and (D) optionally auxiliary agents and additives; wherein the quantity ratio of the components (A) and (B) is measured such that the molar ratio of the NCO groups of the curing agent (A), said groups being provided in the form of uretdione, to the NCO reactive groups of the polyacrylate copolymer (B) equals 3.0:0.5 to 0.5:3.0, and A and B are provided as a physical mixture. The invention additionally relates to a method for producing a polyurethane layer using the aqueous uretdione group-containing composition according to the invention, to the polyurethane layer obtained therefrom, and to a substrate which is coated with or adhered to the polyurethane layer.

The present invention relates to aqueous uretdione group-containing compositions comprising or consisting of

-   -   (A) at least one uretdione group-containing curing agent based         on aliphatic, cycloaliphatic, araliphatic, and/or aromatic         polyisocyanates that contains no chemically-bonded         hydrophilizing groups;     -   (B) at least one polyacrylate copolymer;     -   (C) optionally solvents; and     -   (D) optionally auxiliaries and additives;         -   wherein the quantitative ratio of components (A) and (B) is             such that the molar ratio of the NCO groups of the curing             agent (A) present as uretdione to NCO-reactive groups of the             polyacrylate copolymer (B) is 3:0.5 to 0.5:3, and wherein A             and B are present as a physical mixture.

The invention further relates to a process for producing a polyurethane layer using the aqueous uretdione group-containing composition of the present invention, to the polyurethane layer obtained therefrom, and to a substrate that is coated or bonded with said polyurethane layer.

Recent years have seen a sharp rise in the profile of aqueous paints and coating compositions in the wake of increasingly stringent emissions directives governing the solvents given off when applying paints. Although for many fields of application there are now aqueous coating systems available, these systems are often unable to attain the high quality level of conventional, solvent-based paints in respect of resistance to solvents and chemicals or elasticity and mechanical durability. In particular, there has been no disclosure to date of any polyurethane-based coating compositions that can be processed from an aqueous phase and that go far enough towards satisfying the exacting requirements of the art. This statement applies both to DE 4001783 A1, which relates to special anionically modified aliphatic polyisocyanates, and to the systems of DE 2456469 A1, DE 2814815 A1, EP 0012348 A1, and EP 0424697 A1, which describe aqueous, one-component baking-enamel binders based on blocked polyisocyanates and organic polyhydroxy compounds.

In recent years, further improvements to one-component baking-enamel binders based on blocked polyisocyanates have been achieved, as described for example in EP 0576952 A.

The above one-component baking-enamel binders of the prior art that are based on blocked polyisocyanates have the disadvantage, even if they are largely solvent-free, that the blocking agents are released when the enamel binders are baked, which in turn contributes to emissions.

There has consequently long been a market demand for developing aqueous, emission-free one-component baking-enamel binders. There has been no shortage of attempts at producing such baking-enamel binders based on uretdione-containing polyisocyanates that do not give rise to elimination products.

According to EP 1687354 A1, aqueous uretdione-containing dispersion coatings can be produced by combining a solid uretdione compound with a molten water-dispersible resin, salting the water-dispersible resin if necessary, and dispersing the resin mixture in water. The molten water-dispersible resin may contain a functionality that is reactive toward the uretdione compound, or the coating composition may contain another water-dispersible resin having a functionality that is reactive toward the uretdione compound. In the example, an epoxy resin was however used. Epoxy coatings are generally known to be inferior in most properties to polyurethane coatings. According to EP 1687354 A1, it is also necessary to use an additional emulsifier in the production of these dispersion coatings, which further compromises the coating properties of the dispersion coatings. In addition, the method of production described in EP 1687354 A1 is associated with very high thermal stress on the uretdione groups, which in practice would most likely lead to loss of the uretdione groups. The dispersions described in EP 1687354 A1 were moreover applied immediately, directly after preparation. EP 1687354 A1 provides no information on the stability of these dispersions.

US 2015232609A1 discloses water-dispersible hydrophilic uretdione-containing polyisocyanates obtainable by reacting a prepolymer bearing uretdione groups with an emulsifier containing an ionogenic group, with the ionogenic group having either a pKa of >8 or a pKb of >8 in water at room temperature. Although such uretdione-containing reaction products exhibited an improved storage stability of 8 weeks at room temperature, this is still inadequate for practical uses in industry, where it is not uncommon for transport over long distances to be necessary.

The above problems were surprisingly solved by using a physical mixture of the specific curing agent and the polyacrylate copolymer of the present invention. In particular, dispersions were obtained that show increased storage stability compared to known prior art compositions.

The present invention relates in particular to:

-   -   1. Aqueous uretdione group-containing compositions comprising or         consisting of     -   (A) at least one uretdione group-containing curing agent based         on aliphatic, cycloaliphatic, araliphatic, and/or aromatic         polyisocyanates, preferably based on based on aliphatic,         cycloaliphatic, and/or araliphatic polyisocyanates, more         preferably based on aliphatic and/or cycloaliphatic         polyisocyanates, that contains no chemically-bonded         hydrophilizing groups;     -   (B) at least one polyacrylate copolymer;     -   (C) optionally solvents; and     -   (D) optionally auxiliaries and additives;         -   wherein the quantitative ratio of components (A) and (B) is             such that the molar ratio of the NCO groups of the curing             agent (A) present as uretdione to NCO-reactive groups of the             polyacrylate copolymer (B) is 3.0:0.5 to 0.5:3.0, preferably             2.5:1.0 to 1.0:2.5, more preferably 2.0:1.0 to 1.0:2.0, and             wherein (A) and (B) are present as a physical mixture.     -   2. Aqueous uretdione group-containing composition according to         aspect 1, characterized in that the at least one uretdione         group-containing curing agent (A) was obtained by reacting         monomeric isocyanates comprising or consisting of at least one         monomeric isocyanate selected from tetramethylene diisocyanate,         cyclohexane-1,3-diisocyanate and cyclohexane-1,4-diisocyanate,         pentamethylene diisocyanate, hexamethylene diisocyanate (HDI),         1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane         (isophorone diisocyanate IPDI),         dicyclohexylmethane-2,4′-diisocyanate and/or         dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene         diisocyanate (TMXDI), triisocyanatononane, tolylene diisocyanate         (TDI), diphenylmethane-2,4′-diisocyanate and/or         diphenylmethane-4,4′-diisocyanate (MDI),         triphenylmethane-4,4′-diisocyanate or         naphthylene-1,5-diisocyanate or mixtures thereof, preferably         from isophorone diisocyanate,         dicyclohexylmethane-2,4′-diisocyanate and/or         dicyclohexylmethane-4,4′-diisocyanate, or hexamethylene         diisocyanate.     -   3. Aqueous uretdione group-containing composition according to         aspect 1 or 2, characterized in that hydroxyl-containing         monomers and/or polymers are used as starting materials for the         at least one uretdione group-containing curing agent (A).     -   4. Aqueous uretdione group-containing composition according to         any of the preceding aspects, characterized in that the at least         one uretdione group-containing curing agent (A) has a free NCO         content of less than 5% by weight and a content of uretdione         groups of 1% to 18% by weight—calculated as C₂N₂O₂, molecular         weight 84 g/mol.     -   5. Aqueous uretdione group-containing composition according to         any of the preceding aspects, characterized in that the aqueous         composition has an acid value of 1 to 100 mg KOH/g, preferably 2         to 50 mg KOH/g, more preferably 5 to 30 mg KOH/g, preferably         measured in accordance with DIN EN ISO 2114: 2002-06 with         acetone and ethanol in a weight ratio of 2:1 as solvent, and         calculated based on the solids content.     -   6. Aqueous uretdione group-containing composition according to         any of the preceding aspects, characterized in that         -   the at least one polyacrylate copolymer (B) is obtained by             reacting a mixture of free-radically polymerizable monomers             (M), comprising or consisting of         -   (M1) hydroxyl- and carboxyl-free (meth)acrylic esters having             C1 to C12 hydrocarbon radicals in the alcohol moiety;         -   (M2) hydroxyl-functional, free-radically polymerizable             monomers;         -   (M3) carboxyl-functional, free-radically polymerizable             monomers;         -   (M4) optionally vinyl esters of aliphatic carboxylic acids;         -   (M5) optionally at least one cycloaliphatic ester of             (meth)acrylic acid and/or vinylaromatics.     -   7. Aqueous uretdione group-containing composition according to         any of the preceding aspects, characterized in that         -   the polyacrylate copolymer (B) containing at least one             hydroxyl group has an OH content greater than 1% by             weight—calculated as OH groups based on the solids content,             molecular weight 17 g/mol—and a number-average molecular             weight Mn of 500 to 20 000 g/mol.     -   8. Aqueous uretdione dispersion according to any of the         preceding aspects, characterized in that         -   the solvent is selected from acetone, methyl ethyl ketone,             ethyl acetate, butyl acetate, xylene, solvent naphtha, such             as the commercially available Solvesso 100 or Solvesso 150,             propylene glycol mono-n-butyl ether, dipropylene glycol             dimethyl ether, methoxypropyl acetate, dibasic esters or             mixtures thereof.     -   9. Aqueous uretdione dispersion according to any of the         preceding aspects, characterized in that         -   the auxiliaries and additives are selected from the group             consisting of leveling agents, for example polysilicones or             acrylates, light stabilizers, for example sterically             hindered amines, catalysts, for example tin(II)             2-ethylhexanoate or dibutyltin dilaurate, fillers, and             pigments, for example titanium dioxide, or mixtures thereof.     -   10. Aqueous uretdione group-containing composition according to         any of the preceding aspects, characterized in that         -   the sum of the proportions by weight of (A), (B), and (D) is             30% to 60% by weight based on the solids content of the             total aqueous composition.     -   11. A process for producing a polyurethane layer comprising the         steps of         -   i) providing an aqueous uretdione group-containing             composition according to any of aspects 1 to 10;         -   ii) applying to a substrate the mixture obtained in i);         -   iii) drying the mixture from step ii), and         -   iv) curing the mixture from step iii) by heating to from             40° C. to 180° C. for up to 180 minutes.     -   12. The process according to aspect 11, characterized in that         the aqueous uretdione group-containing composition was obtained         by mixing the uretdione group-containing curing agent (A) with         the at least one polyacrylate copolymer (B) in the absence of         water and subsequently dispersing the mixture with water.     -   13. A polyurethane layer, in particular polyurethane film,         obtainable by a process according to aspect 11 or 12.     -   14. A substrate that is coated or bonded with the polyurethane         layer according to aspect 13.

Unless explicitly stated otherwise, molecular weights in the present invention are determined by GPC (gel-permeation chromatography) using polystyrene standards. The average molecular weight is according to this invention defined as the number-average molecular weight Mn. The Mn is determined at 23° C. in tetrahydrofuran as solvent. The measurement is carried out as described in DIN 55672-1:2007-08: “Gel permeation chromatography, Part 1—Tetrahydrofuran as eluent” using a Security GPC system from PSS Polymer Service, flow rate 0.6 ml/min.

Unless explicitly stated otherwise, % by weight in the present invention refers to the total weight of the respective system or the total weight of the respective component. For example, a copolymer may have a content of a particular monomer that is expressed in % by weight, in which case the percent by weight values would be based on the total weight of the copolymer.

Unless explicitly stated otherwise, the expression “at least one” refers to the type of compound and not to individual molecules. For example, at least one copolymer is to be understood as meaning that at least one type of copolymer is present, but is present in the composition in an indeterminate number of molecules. Hence it is also possible for two or more types of copolymer to be present, in each case in an indeterminate number if the amounts are not defined.

In a preferred embodiment, the aqueous uretdione group-containing composition is substantially free of any other co-emulsifier (in addition to component (B)). The term “substantially free of” is according to the present invention defined as meaning that the composition contains preferably less than 1% by weight, more preferably less than 0.25% by weight, even more preferably less than 0.1% by weight, most preferably less than 0.01% by weight or no content at all of the respective compound, in each case based on the total weight of the aqueous uretdione group-containing composition.

The aqueous uretdione group-containing composition of the present invention is preferably a polyurethane-based composition.

Suitable uretdione group-containing polyisocyanates as starting compounds for component (A) are polyisocyanates that contain at least one isocyanate group and at least one uretdione group. These are prepared through the reaction of suitable starting isocyanates (al) as described for example in WO 02/92657 A1 or WO 2004/005364 A1. In this reaction, some of the isocyanate groups are converted into uretdione groups under catalysts, for example with triazolates or 4-dimethylaminopyridine (DMAP) as catalysts. Examples of isocyanates (al) from which the uretdione-containing structural units are constructed are tetramethylene diisocyanate, cyclohexane-1,3-diisocyanate and cyclohexane-1,4-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate IPDI), dicyclohexylmethane-2,4′-diisocyanate and/or dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene diisocyanate (TMXDI), triisocyanatononane, tolylene diisocyanate (TDI), diphenylmethane-2,4′-diisocyanate and/or diphenylmethane-4,4′-diisocyanate (MDI), triphenylmethane-4,4′-diisocyanate or naphthylene-1,5-diisocyanate, and any desired mixtures of such isocyanates. Preference is given to isophorone diisocyanate, dicyclohexylmethane 2,4′-diisocyanate and/or dicyclohexylmethane 4,4′-diisocyanate or hexamethylene diisocyanate.

In addition to the isocyanate groups and uretdione groups, component (A) may also contain isocyanurate, biuret, allophanate, urethane, and/or urea structures.

The conversion of these uretdione group-bearing polyisocyanates into uretdione group-containing curing agents (A) involves the reaction of the free NCO groups of the abovementioned polyisocyanates with a polyol component (b1), optionally with the additional use of the polyol component (b2).

The polyol component (b1) preferably has a hydroxy group functionality of ≥2 and a molecular weight M_(n) of 62 to 500 g/mol, preferably 62 to 400 g/mol, more preferably 62 to 300 g/mol. The polyol component (b1) preferably contains dihydric to hexahydric polyol components having a molecular weight Mn of 62 to 500 g/mol, preferably 62 to 400 g/mol, more preferably 62 to 300 g/mol. Examples of preferred polyol components (b1) are 1,4-butanediol and/or 1,3-butanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, polyester polyols and/or polyether polyols having an average molecular weight M_(n) of less than or equal to 500 g/mol.

Suitable linear difunctional polyols (b2) are selected from the group consisting of polyethers, polyesters, polycaprolactone diols, and/or polycarbonates. The polyol component (b2) preferably comprises at least one diol containing ester groups and having a molecular weight Mn of 350 to 4000 g/mol, preferably of 350 to 2000 g/mol, more preferably of 350 to 1000 g/mol, The ester diols are generally mixtures in which individual constituents having a molecular weight below or above these limits may also be present in minor amounts. These are the polyester diols known per se that are constructed from diols and dicarboxylic acids.

Examples of suitable diols are 1,4-dimethylolcyclohexane, 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, and pentaerythritol, and mixtures of such diols. Examples of suitable dicarboxylic acids are aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid, cycloaliphatic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, and the anhydrides thereof, and aliphatic dicarboxylic acids, which are used with preference, for example succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, and sebacic acid or the anhydrides thereof.

Polyester diols based on adipic acid, phthalic acid, isophthalic acid, and tetrahydrophthalic acid are preferably used as component (b2). Examples of preferred diols used are 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol or trimethylolpropane, and mixtures thereof.

Also preferable as component (b2) are polycaprolactone diols having an average molecular weight of 350 to 4000 g/mol, preferably of 350 to 2000 g/mol, more preferably of 350 to 1000 g/mol, that are prepared in a manner known per se starting from a diol or diol mixture of the type mentioned above by way of example, and lactones such as β-propiolactone, γ-butyrolactone, γ- and δ-valerolactone, ε-caprolactone, 3,5,5- and 3,3,5-trimethylcaprolactone, for example, or any desired mixtures of such lactones. Particular preference is given to such polycaprolactone diols that are prepared by polymerizing ε-caprolactone.

(Co)polyethers of ethylene oxide, propylene oxide, and/or tetrahydrofuran containing less than 30 mol % of ethylene oxide units may also be used as the linear polyol component (b2). Preference is given to polyethers having an average molar weight Mn of 500 to 2000 g/mol, for example polypropylene oxides or polytetrahydrofuran diols.

Also suitable as (b2) are hydroxyl-containing polycarbonates, preferably having an average molar weight Mn of 400 to 4000 g/mol, preferably of 400 to 2000 g/mol, for example hexanediol polycarbonate and polyester carbonates.

The polyol component (b2) used in the preparation of the uretdione group-containing curing agents (A) may also take the form of diols containing low-molecular-weight ester groups and having an average molecular weight, calculable from the functionality and hydroxyl value, of 134 to 349 g/mol, preferably 176 to 349 g/mol. Examples of these include the diols containing ester groups that are known per se, or mixtures of such diols, as can be prepared for example by reacting alcohols with substoichiometric amounts of dicarboxylic acids, corresponding dicarboxylic anhydrides, corresponding dicarboxylic esters of lower alcohols or lactones. Examples of suitable acids are succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic acid, maleic acid, maleic anhydride, dimethyl terephthalate, and bisglycol terephthalate. Examples of suitable lactones for preparing said ester diols are β-propiolactone, γ-butyrolactone, γ- and δ-valerolactone, ε-caprolactone, 3,5,5- and 3,3,5-trimethylcaprolactone or any desired mixtures of such lactones.

Amino-functional compounds may also be used in the preparation of the uretdione group-containing curing agents (A). Examples of suitable low-molecular-weight amino-functional compounds are aliphatic and cycloaliphatic amines and amino alcohols containing primary and/or secondary amino groups, for example cyclohexylamine, 2-methyl-1,5-pentanediamine, diethanolamine, monoethanolamine, propylamine, butylamine, dibutylamine, hexylamine, monoisopropanolamine, diisopropanolamine, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, isophoronediamine, diethylenetriamine, ethanolamine, aminoethylethanolamine, diaminocyclohexane, hexamethylenediamine, methyliminobispropylamine, iminobispropylamine, bis(aminopropyl)piperazine, aminoethylpiperazine, 1,2-diaminocyclohexane, triethylenetetramine, tetraethylenepentamine, bis(4-aminocyclohexyl)methane, bis(4-amino-3-methylcyclohexyl)methane, bis(4-amino-3,5-dimethylcyclohexyl)methane, bis(4-amino 2,3,5-trimethylcyclohexyl)methane, 1,1-bis(4-aminocyclohexyppropane, 2,2-bis(4-aminocyclohexyl)propane, 1,1-bis(4-aminocyclohexyl) ethane, 1,1-bis(4-aminocyclohexyl)butane, 2,2-bis(4-aminocyclohexyl)butane, 1,1-bis(4-amino-3-methylcyclohexyl) ethane, 2,2-bis(4-amino-3-methylcyclohexyl)propane, 1,1-bis(4-amino-3,5-dimethylcyclohexyl)ethane, 2,2-bis(4-amino-3,5-dimethylcyclohexyppropane, 2,2-bis(4-amino-3,5-dimethylcyclohexyl)butane, 2,4-diaminodicyclohexylmethane, 4-aminocyclohexyl-4-amino-3-methylcyclohexylmethane, 4-amino-3,5-dimethylcyclohexyl-4-amino-3-methylcyclohexylmethane, and 2-(4-aminocyclohexyl)-2-(4-amino-3-methylcyclohexyl)methane.

Solvents may optionally be used in the preparation of the uretdione group-containing curing agents (A). Suitable as solvent for the uretdione group-containing curing agents (A) are all liquid substances that do not react with other constituents, for example acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, such as the commercially available Solvesso 100 and Solvesso 150, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters or mixtures thereof.

The uretdione group-containing curing agents (A) are substantially free of ionic or nonionic, chemically bonded hydrophilizing groups. Ionically hydrophilizing groups are understood by those skilled in the art as meaning groups having the capability of forming anions or cations. Groups capable of forming anions or cations are those that can be converted into an anionic or cationic group through chemical reaction, in particular through neutralization.

The uretdione group-containing curing agents (A) are preferably free of carboxyl group-containing polyols or diols capable of anion formation, for example dihydroxycarboxylic acids such as α,α-dialkylolalkanoic acids, in particular α,α-dimethylolalkanoic acids such as 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, or polyhydroxy acids such as gluconic acid. In addition, the uretdione group-containing curing agents (A) are preferably free of compounds containing amino groups and capable of anion formation such as α,Ω-diaminovaleric acid or 2,4-diaminotoluenesulfonic acid. The uretdione group-containing curing agents (A) are also preferably free of sulfonic acid groups capable of anion formation.

The uretdione group-containing curing agents (A) are additionally preferably free of compounds capable of cation formation from the group consisting of tertiary amino or ammonium compounds, for example tris(hydroxyalkyl)amines, N,N′-bis(hydroxyalkyl)alkylamines, N-hydroxyalkyldialkylamines, trisaminoalkylamines, N,N′-bis(aminoalkyl)alkylamines, N-aminoalkyldialkylamines, and mixtures thereof.

The uretdione group-containing curing agents (A) are further preferably free of nonionically hydrophilizing compounds such as for example polyalkylene oxide polyether alcohols or polyalkylene oxide polyether amines. In particular, the uretdione group-containing curing agents (A) are preferably free of polyethylene oxide polyethers or mixed polyalkylene oxide polyethers in which 30 mol % or more of the alkylene oxide units consist of ethylene oxide units.

Preferred uretdione group-containing curing agents (A) have a free NCO content of less than 5% by weight and a content of uretdione groups of 1% to 18% by weight (calculated as C₂N₂O₂, molecular weight 84 g/mol). In addition to the uretdione groups, the curing agents (A) may also contain isocyanurate, biuret, allophanate, urethane, and/or urea structures.

The composition also comprises at least one polyacrylate copolymer (component (B)). In accordance with the present invention, the term “polyacrylate copolymer” encompasses both polyacrylate copolymers and poly(meth)acrylate copolymers.

Suitable polyacrylate copolymers may be obtained, for example, by the synthesis of the following mixture of free-radically polymerizable monomers (M):

-   -   (M1) hydroxyl- and carboxyl-free (meth)acrylic esters having C1         to C12 hydrocarbon radicals in the alcohol moiety;     -   (M2) hydroxyl-functional, free-radically polymerizable monomers;     -   (M3) carboxyl-functional, free-radically polymerizable monomers;     -   (M4) optionally vinyl esters of aliphatic carboxylic acids;     -   (M5) optionally at least one cycloaliphatic ester of         (meth)acrylic acid and/or vinylaromatics.

The mixture may further comprise polyols (PO) selected from the group consisting of polyester polyols and/or polycarbonate polyols, the polyols having an average hydroxyl group functionality of at least two.

The polyacrylate dispersions of the invention can have high hydroxyl group contents, which means that—without being bound to a particular theory—a higher degree of crosslinking and thus higher hardness can be achieved in the resulting coatings.

In the context of the present invention, acrylic acid or methacrylic acid are also referred to as (meth)acrylic acid.

Acrylates and methacrylates having 1 to 18 carbon atoms in the alcohol component of the ester group are used as monomers (M1) free of hydroxyl and carboxyl groups. The alcohol moiety is preferably aliphatic and may be linear or branched.

Examples of suitable monomers for component (M1) are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, the isomeric pentyl, hexyl, 2-ethylhexyl, octyl, and dodecyl (meth)acrylates. Preferred monomers (M1) are methyl, n-butyl, isobutyl, tert-butyl (meth)acrylate and also 2-ethylhexyl acrylate and styrene.

Suitable hydroxy-functional monomers (M2) are ethylenically unsaturated, hydroxyl-containing monomers such as hydroxyalkyl esters of unsaturated carboxylic acids, preferably hydroxyalkyl (meth)acrylates having 2 to 12, preferably 2 to 6, carbon atoms in the hydroxyalkyl radical. Examples of particularly preferred compounds are 2-hydroxyethyl (meth)acrylate, the isomeric hydroxypropyl (meth)acrylates, 2-, 3-, and 4-hydroxybutyl (meth)acrylates, and the isomeric hydroxyhexyl (meth)acrylates. Preference is given to 4-hydroxybutyl acrylate (butanediol monoacrylate) and hydroxyethyl methacrylate.

Suitable carboxyl-functional free-radically polymerizable monomers (M3) are olefinically unsaturated monomers that contain carboxylic acid or carboxylic anhydride groups, such as acrylic acid, methacrylic acid, beta-carboxyethyl acrylate, crotonic acid, fumaric acid, maleic anhydride, itaconic acid or monoalkyl esters of dibasic acids or anhydrides, for example maleic acid monoalkyl esters. Preference is given to acrylic acid and/or methacrylic acid.

Suitable vinyl esters of aliphatic carboxylic acids (M4) may be included. Examples of such monomers are the esterification products of vinyl alcohol with linear or branched, aliphatic carboxylic acids such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl octanoate, vinyl decanoate, vinyl neodecanoate, vinyl dodecanoate (vinyl laurate) or vinyl stearate.

Examples of suitable monomers (M5) are cyclohexyl (meth)acrylate, cyclohexyl (meth)acrylates having alkyl ring substituents, 4-tert-butylcyclohexyl (meth)acrylate, norbornyl (meth)acrylate, and isobornyl (meth)acrylate, with preference given to isobornyl acrylate and/or isobornyl methacrylate, and particular preference to isobornyl methacrylate. It is also possible to use mixtures comprising isobornyl acrylate and isobornyl methacrylate and other monomers (M5). Particularly suitable vinyl aromatics are styrene, optionally substituted styrenes, and vinyltoluenes. Monomers (M5) other than isobornyl acrylate and isobornyl methacrylate may optionally be used in amounts of less than 10% by weight based on the total weight of (M1) to (M5).

Further monomers (M6) such as acetoacetoxyethyl methacrylate, acrylamide, acrylonitrile, vinyl ether, methacrylonitrile or vinyl acetates may optionally also be included. In addition, it is possible to use proportions of monofunctional polyalkylene oxides having molecular weights of 200 to 3000 g/mol, preferably 350 to 1000 g/mol, or esterified (meth)acrylic acid, that are suitable as nonionic, hydrophilic groups. Suitable alkylene oxides include preferably ethylene oxide or mixtures of ethylene oxide and propylene oxide. However, it is preferable when hydrophilization of the copolymers is by means of ionic groups, that is to say monomers (M3).

The proportions of monomers (M1) to (M6) may be chosen such that the polyacrylate copolymer has an OH value (DIN EN ISO 4629-1:2016-12) of 50 to 400 mg KOH/g, preferably of 100 to 300 mg KOH/g solids. In the case of the polyester polyols and/or polycarbonate polyols (PO), it is preferable that the average hydroxyl group functionality is at least 2.5. Suitable polyester polyols are the known polycondensates of polyols (triols, tetraols) with dicarboxylic and optionally polycarboxylic acids (tricarboxylic/tetracarboxylic acids) or hydroxycarboxylic acids or lactones.

In the preparation of the polyesters it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols instead of the free polycarboxylic acids. Examples of suitable alcohols are trimethylolpropane, glycerol, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurate.

Examples of suitable dicarboxylic include phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, tetrachlorophthalic acid, maleic acid, fumaric acid, itaconic acid acid, malonic acid, suberic acid, 2-methylsuccinic acid, 3,3-diethylglutaric acid, and 2,2-dimethylsuccinic acid. The possible anhydrides of these acids are likewise suitable. For the purposes of the present invention, the anhydrides are consequently encompassed by the term “acid”. It is also possible to use monocarboxylic acids such as benzoic acid, hexanecarboxylic acid or fatty acids, provided the average functionality of the polyol is greater than two. Saturated aliphatic or aromatic acids are preferred, such as adipic acid or isophthalic acid. Polycarboxylic acids such as trimellitic acid may be used in relatively small amounts. Examples of hydroxycarboxylic acids that may be used as reactants in the preparation of a polyester polyol having a terminal hydroxyl group include hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid, or hydroxystearic acid. Examples of suitable lactones include ε-caprolactone or butyrolactone.

The suitable hydroxyl-containing polycarbonates can be obtained by reacting carbonic acid derivatives, for example diphenyl carbonate, dimethyl carbonate or phosgene, with polyols. Examples include ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-bis(hydroxymethyl)cyclohexane, 2-methyl 1,3-propanediol, 2,2,4-trimethylpentane-1,3-diol, dipropylene glycol, polypropylene glycols, dibutylene glycol, polybutylene glycols, bisphenol A, tetrabromobisphenol A, but also lactone-modified diols. The diol component preferably contains 40% to 100% by weight of hexanediol, preferably 1,6-hexanediol and/or hexanediol derivatives, particularly preferably those containing ether or ester groups in addition to terminal OH groups. In order to obtain the desired functionality of at least 2, the polycarbonate polyols contain branching through the incorporation of polyfunctional components, in particular low-molecular-weight polyols.

Examples of compounds suitable for this purpose include glycerol, trimethylolpropane, hexane-1,2,6-triol, butane-1,2,4-triol, trimethylolpropane, pentaerythritol, quinitol, marinitol, and sorbitol, methyl glycoside or 1,3,4,6-dianhydrohexitols. The polyacrylate copolymer can in principle be produced by means of conventional free-radical polymerization processes in the organic phase. The polyacrylate copolymer is preferably produced in a multistage process, as has been previously described in EP-A 0 947 557 or in EP-A 1 024 184. In this process, a hydrophobic monomer mixture that is free of acid groups or has a low content of acid groups is first metered in, after which, at a later point in time in the polymerization, a more hydrophilic monomer mixture containing acid groups is metered in, with the more hydrophilic monomer mixture containing acid groups that do not contain any monomers of type (M4) and (M5). The copolymerization is generally carried out at 40 to 180° C., preferably at 80 to 160° C. Suitable initiators (I) for the polymerization reaction include organic peroxides, for example di-tert-butyl peroxide or tert-butyl peroxy-2-ethylhexanoate, and azo compounds.

The amounts of initiator used depend on the desired molecular weight. For reasons of operational safety and easier handling, it is also possible for peroxide initiators to be used in the form of a solution in suitable organic solvents of the type already specified. The rate of addition of the initiator (I) in the method of the invention can be regulated such that it lasts until the end of the monomer feed, and the amounts of solvent in steps one and two are chosen such that an organic solvent content of less than 20% by weight results.

The amounts of the constituents are preferably calculated such that a mass ratio (M1):(M2) from 9:1 to 6:1, more preferably a mass ratio (M1):(M2) from 4:1 to 3:1, results. Likewise preferable is a (M1):(M3) from 50:1 to 40:1, more preferably a (M1):(M3) from 35:1 to 30:1. Likewise preferable is a (M1):(M5) from 9:1 to 6:1, more preferably a (M1):(M5) from 6:1 to 5:1.

The free-radical polymerization may be carried out in the presence of a solvent or solvent/water mixture that is added to the reaction vessel. All solvents known in coatings technology are suitable as organic solvents, preference being given to those that are customarily used as cosolvents in aqueous dispersions, for example alcohols, ethers, ethers containing ether groups, esters, ketones or nonpolar hydrocarbons or mixtures of these solvents. The solvents are used in such amounts that their proportion in the finished dispersion is 0% to 20% by weight, preferably 0.1% to 15% by weight.

It is also possible to produce the polyacrylate copolymer by the process described in EP-A 1 024 184, using a hydrophobic copolymer as the initial charge. Instead of a multistage polymerization process, it is also possible to execute the process of the invention continuously (gradient polymerization), that is to say a monomer mixture having a changing composition is added, the fractions of hydrophilic (acid-functional) monomer being higher at the end of the feed than at the start. The number-average molecular weight Mn of the polyacrylate copolymers can be set by means of a specific choice of operating parameters, for example the molar ratio of monomer to initiator, for example the reaction time or the temperature, to generally between 500 g/mol and 30 000 g/mol, preferably between 1000 g/mol and 15 000 g/mol, more preferably between 1500 g/mol and 10 000 g/mol. The hydroxyl group content of the polyacrylate copolymers is in 100% form preferably 1.5% to 12.0% by weight, more preferably 2.0% to 10.0% by weight, and particularly preferably 1.5% to 9.0% by weight.

Before, during or after the mixing of the polyacrylate copolymers with the at least one uretdione-containing curing agent (A), the acid groups present in the polyacrylate copolymers are at least partially converted into their salt form, preferably through addition of suitable neutralizing agents. Suitable neutralizing agents are organic amines or water-soluble inorganic bases, for example soluble metal hydroxides, metal carbonates, or metal hydrogen carbonates, for example sodium hydroxide or potassium hydroxide.

Examples of suitable amines are butyldiethanolamine, N-methylmorpholine, triethylamine, ethyldiisopropylamine, N,N-dimethylethanolamine, N,N-dimethylisopropanolamine, N-methyldiethanolamine, diethylethanolamine, triethanolamine, butanolamine, morpholine, 2-aminomethyl-2-methylpropanolamine or isophoronediamine. In mixtures it is also possible to use a proportion of ammonia. Particular preference is given to triethanolamine, N,N-dimethylethanolamine, and ethyldiisopropylamine.

In one embodiment, the mixture of free-radically polymerizable monomers (M) does not contain: (M4) vinyl esters of aliphatic carboxylic acids. Examples of such monomers to be avoided are the esterification products of vinyl alcohol with linear or branched aliphatic carboxylic acids such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl octanoate, vinyl decanoate, vinyl neodecanoate, vinyl dodecanoate (vinyl laurate) or vinyl stearate.

In a further embodiment, the mixture of free-radically polymerizable monomers (M) does not contain: (M5): cycloaliphatic esters of (meth)acrylic acid and/or vinylaromatics. Examples of such monomers to be avoided are cyclohexyl (meth)acrylate, cyclohexyl (meth)acrylates having alkyl ring substituents, 4-tert-butylcyclohexyl (meth)acrylate, norbornyl (meth)acrylate, isobornyl (meth)acrylate, isobornyl acrylate and/or isobornyl methacrylate and/or mixtures of the abovementioned monomers.

In another embodiment, the polyacrylate copolymer has in 100% form a hydroxyl group content of >1.5% by weight to <12.0% by weight, preferably from >2.0% by weight to <10.0% by weight. The hydroxyl group content may be calculated by dividing the hydroxyl value, determined as described above, by 33.

In a further embodiment, the polyols (PO) have a hydroxyl group content of >15% by weight to <35% by weight, preferably from >20% by weight to <30% by weight. The hydroxyl group content may be calculated by dividing the hydroxyl value, determined as described above, by 33.

In a further embodiment, the polyols (PO) are polyester polyols obtained from the reaction of an at least trifunctional alcohol with a lactone. A particularly preferred polyol is obtained from trimethylolpropane and ε-caprolactone. For example, trimethylolpropane and ε-caprolactone may be reacted in a weight ratio of >60:40 to <80:20, preferably >68:32 to <72:28. Optionally, the reaction can take place in the presence of a catalyst.

In a further embodiment, the monomers (M1), (M2), (M3), (M4), and (M5) are used in the following amounts:

(M1) >25% by weight to <90% by weight, preferably >30% by weight to <80% by weight,

(M2) >8% by weight to <50% by weight, preferably >30% by weight to <45% by weight,

(M3) >1% by weight to <10% by weight, preferably >2% by weight to <5% by weight,

optionally (M4) >1% by weight to <10% by weight, preferably >1.5% by weight to <5% by weight,

optionally (M5) >5% by weight to <40% by weight, preferably >10% by weight to <35% by weight; and optionally the polyols (PO) in amounts of >5% by weight to <20% by weight, preferably >8% by weight to <15% by weight, based on the total weight of the solids in the dispersion, the amounts stated adding up to 100% by weight.

The polyurethane resin used according to the invention is preferably produced in such a way that a polyacrylate copolymer (B) is mixed homogeneously in a non-aqueous system with at least one uretdione group-containing curing agent (A) based on aliphatic, (cyclo)aliphatic, araliphatic, and/or aromatic polyisocyanates that contains no chemically bonded hydrophilizing groups. After this, the carboxyl groups present in the polyacrylate copolymer (B) are neutralized with suitable neutralizing agents preferably to at least 50%, more preferably 80% to 130%, particularly preferably 95 to 125%, and then dispersed with deionized water. The neutralization can take place before, during or after the dispersion step. Neutralization before the addition of water is, however, preferred.

Examples of suitable neutralizing agents are triethylamine, dimethylaminoethanol, dimethylcyclohexylamine, triethanolamine, methyldiethanolamine, diisopropanolamine, ethyldiisopropylamine, diisopropylcyclohexylamine, N-methylmorpholine, 2-amino-2-methyl-1-propanol, ammonia or other customary neutralizing agents or neutralizing mixtures thereof.

Preference is given to amines such as triethylamine, triethanolamine, diisopropylhexylamine, and dimethylethanolamine, and particular preference to triethanolamine and dimethylethanolamine.

In accordance with the present invention, the neutralizing agents are to be included in the group of auxiliaries and additives (D).

Suitable as solvents under (C) are all liquid substances that do not react with other constituents. Preference is given to acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, such as the commercially available Solvesso 100 and Solvesso 150, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters or mixtures thereof. The solvent used may then optionally be removed by distillation.

In accordance with the invention, additives (D) that are customary in coatings and adhesives technology, for example leveling agents such as polysilicones or acrylates, light stabilizers such as sterically hindered amines, catalysts, for example tin(II) 2-ethylhexyl octoate or dibutyltin dilaurate, or other auxiliaries such those described in EP 0 669 353, may be present in a total amount of preferably 0.05% to 5% by weight. Fillers and pigments such as titanium dioxide may be added to the aqueous composition in an amount of up to 50% by weight.

EXAMPLES

Raw Materials Employed:

Dowanol PnB: propylene glycol mono-n-butyl ether, from Dow

Peroxan DB: di-tert-butyl peroxide from Pergan.

Solvent Naphtha 100: an aromatic solvent, CAS: 64 742-95-6, from Azelis.

Veova 9: Versatic acid vinyl ester from Momentive.

Analytical Methods Used:

All viscosity measurements were carried out using a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) in accordance with DIN EN ISO 3219:1994-10.

NCO contents were determined titrimetrically in accordance with DIN EN ISO 11909:2007-05.

OH values were determined titrimetrically in accordance with DIN EN ISO 4629-2:2015-02.

The determination of acid values titrimetrically in accordance with DIN EN ISO 2114:2002-06.

Solids contents were determined in a circulating-air oven in accordance with DIN EN ISO 3251:2008-06, method B.

Average particle sizes (MPS) were determined using a Zetasizer Nano from Malvern (DE) in accordance with DIN ISO 13321:2004-10.

pH determinations were carried out using a pH meter in accordance with DIN ISO 976:2008-07 in a 1:4 dilution with distilled water.

Residual monomer contents were measured in accordance with DIN EN ISO 10283 by gas chromatography with an internal standard.

Pendulum hardness was measured on a standardized coil test plate (coil coating black—CS 200570, from Heinz Zanders Prüf-Blech-Logistik) in accordance with DIN EN ISO 1522:2007-04 using a König pendulum.

Chemical resistance was measured on a standardized coil test plate (coil coating black—CS 200570, from Heinz Zanders Prüf-Blech-Logistik). A cotton pad soaked in the test substance (xylene or water) was laid on the coating surface and covered with a watch glass. After the specified contact time, the cotton pad soaked in test substance was removed and the contact site dried off and immediately examined. Softening and discoloration of the coating surface were assessed. The assessment was made in accordance with DIN EN ISO 4628-1 as follows:

0 no, i.e. no noticeable damage

1 very few areas of damage, i.e. small, just about significant number

2 a few areas of damage, i.e. small, but significant number

3 moderate number of areas of damage

4 considerable number of areas of damage

5 very many areas of damage

Unless explicitly described otherwise, all percentages refer to percentages by weight.

Preparation of a Uretdione Group-Containing Crosslinker (Crosslinker 1, Preparation Example)

To 1000 g (4.50 mol) of isophorone diisocyanate (IPDI) were successively added at room temperature under dry nitrogen, with stirring, 10 g (1%) of triisodecyl phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as catalyst. After 20 h, the reaction mixture, which had an NCO content of 28.7%, corresponding to a degree of oligomerization of 21.8%, was freed of volatiles, without prior addition of a catalyst poison, with the aid of a thin-film evaporator at a temperature of 160° C. and a pressure of 0.3 mbar.

This yielded a light yellow uretdione polyisocyanate having a free NCO group content of 17.0%, a monomeric IPDI content of 0.4%, and a viscosity of more than 200 000 mPas.

337 g of 1,4-butanediol, 108 of 2-ethylhexanol, and 569 g of ε-caprolactone were mixed at room temperature under dry nitrogen, 0.3 g of tin(II) octoate was added, and the mixture was stirred at 160° C. for 5 h and then cooled to room temperature. To this mixture was then added, over a period of 30 min, 1850 g of the above-described uretdione group-containing polyisocyanate based on IPDI, which was warmed to 80° C. The reaction mixture was stirred at a temperature of max. 100° C. until the NCO content of the reaction mixture had fallen to a value of 0.8% after 7 to 8 h. The reaction mixture was solidified by pouring it onto a metal sheet, comminuted, and then dissolved in Dowanol PnB to give a solution with a solids content of 60% by weight.

Examples 1 to 4 Example 1

TABLE 1 Weight (g) Component 1 DOWANOL PnB 1567 Component 2 PEROXAN DB 33 DOWANOL PnB 33 Component 3 METHYL METHACRYLATE 1243 HYDROXYETHYL METHACRYLATE 2419 n-BUTYL METHACRYLATE 592 n-BUTYL ACRYLATE 723 ISOBORNYL METHACRYLATE 1701 BUTANEDIOL MONOACRYLATE 836 STYRENE 573 Component 4 PEROXAN DB 140 DOWANOL PnB 140 Component 5 BUTANEDIOL MONOACRYLATE 296 METHYL METHACRYLATE 449 HYDROXYETHYL METHACRYLATE 467 n-BUTYL ACRYLATE 379 ACRYLIC ACID 316 Component 6 PEROXAN DB 33 DOWANOL PnB 60 Total amount 12000

Component 1 from table 1 was weighed into a stirring apparatus under nitrogen and heated to 138° C. Component 2 was then metered in evenly at 138° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in evenly at 138° C. in parallel over a period of 4 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for 30 min. Finally, component 5 and component 6 were metered in evenly at 138° C. in parallel over a period of 1 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for a further 1 h. After cooling, a pale yellowish, highly viscous polyacrylate solution was obtained. 500 g of this solution was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 567 g of the 60% solution of crosslinker 1 in Dowanol PnB was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of a mixture of 21.5 g of triethanolamine and 4.3 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 463 g of distilled water was stirred in to the mixture. Fine adjustment of the viscosity to approx. 2000 mPas afforded a dispersion having the following properties:

Solids content 43.7% by weight Acid value (100%) 13 mg KOH/g OH content (100%, calculated) 2.8% by weight Average particle size 230 nm Viscosity 2030 mPas pH 7.5 The dispersion remained stable at 23° C. for 10 months.

Example 2

500 g of polyacrylate solution from example 1 was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 283 g of the 60% solution of crosslinker 1 in Dowanol PnB was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of a mixture of 21.5 g of triethanolamine and 4.3 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 407 g of distilled water was stirred into it. Fine adjustment of the viscosity to approx. 2000 mPas afforded a dispersion having the following properties:

Solids content 41.7% by weight Acid value (100%) 16.6 mg KOH/g OH content (100%, calculated) 3.6% by weight Average particle size 175 nm Viscosity 2360 mPas pH 7.5 The dispersion remained stable at 23° C. for 10 months.

Example 3

TABLE 2 Weight (g) Component 1 SOLVENT NAPHTHA 100 900 BUTYLGLYCOL 648 Component 2 PEROXAN DB 33 BUTYLGLYCOL 33 Component 3 METHYL METHACRYLATE 3669 HYDROXYETHYL METHACRYLATE 1816 n-BUTYL ACRYLATE 2603 Component 4 PEROXAN DB 139 BUTYLGLYCOL 139 Component 5 METHYL METHACRYLATE 520 HYDROXYETHYL METHACRYLATE 734 n-BUTYL ACRYLATE 408 ACRYLIC ACID 245 Component 6 PEROXAN DB 33 BUTYLGLYCOL 80 Total amount 12000

Component 1 from table 2 was weighed into a stirring apparatus under nitrogen and heated to 138° C. Component 2 was then metered in evenly at 138° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in evenly at 138° C. in parallel over a period of 4 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for 30 min. Finally, component 5 and component 6 were metered in evenly at 138° C. in parallel over a period of 1 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for a further 1 h. After cooling, a pale yellowish, highly viscous polyacrylate solution was obtained to 100° C., the reaction mixture was transferred to the appropriate container(s).

552 g of this solution was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 471 g of the 60% solution of crosslinker 1 in Dowanol PnB was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of 14.6 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 466 g of distilled water was stirred in. Fine adjustment of the viscosity to approx. 2000 mPas afforded a stable dispersion having the following properties:

Solids content 46.1% by weight Acid value (100%) 16.3 mg KOH/g OH content (100%, calculated) 2.1% by weight Average particle size 225 nm Viscosity 1110 mPas pH 8.2 The dispersion remained stable at 23° C. for 5 months.

Example 4

TABLE 3 Weight (g) Component 1 DOW ANOL PnB 3438 Component 2 PEROXAN DB 33 DOWANOL PnB 33 Component 3 STYRENE 570 METHYL METHACRYLATE 1566 HYDROXYETHYL METHACRYLATE 1601 n-BUTYL ACRYLATE 341 ISOBORNYL METHACRYLATE 1520 n-BUTYL METHACRYLATE 1208 VEOVA 9 1251 Component 4 PEROXAN DB 118 DOWANOL PnB 321 Total amount 12000

Component 1 from table 3 was weighed into a stirring apparatus under nitrogen and heated to 148° C. Component 2 was then metered in evenly at 148° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in evenly at 148° C. in parallel over a period of 6 h. At the end of the addition, the reaction mixture was held at 148° C. for 60 min. After cooling to 80° C., the polyacrylate solution was transferred to the appropriate container(s).

TABLE 4 Raw material Weights Component 1 Polyacrylate solution from table 3 1993 Component 2 PEROXAN DB 36 DOWANOL PnB 36 72 Component 3 2-ETHYLHEXYL ACRYLATE 377 HYDROXYETHYL ACRYLATE 1931 n-BUTYL METHACRYLATE 1308 ISOBORNYL METHACRYLATE 2951 n-BUTYL ACRYLATE 338 BUTANEDIOL MONOACRYLATE 555 Component 4 PEROXAN DB 129 DOWANOL PnB 154 Component 5 METHYL METHACRYLATE 533 HYDROXYETHYL ACRYLATE 799 n-BUTYL ACRYLATE 411 METHACRYLIC ACID 333 Component 6 PEROXAN DB 36 DOWANOL PnB 80 Total amount 12000

Component 1 from table 4 was weighed into a stirring apparatus under nitrogen and heated to 144° C. Component 2 was then metered in evenly at 144° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in evenly at 144° C. in parallel over a period of 4 h 30 min. At the end of the addition, the reaction mixture was held at 144° C. for 5 min. Finally, component 5 and component 6 were metered in evenly at 144° C. in parallel over a period of 1 h 30 min. At the end of the addition, the reaction mixture was held at 144° C. for a further 1 h. After cooling, a pale yellowish, highly viscous polyacrylate solution was obtained.

304 g of this solution was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 385 g of the 60% solution of crosslinker 1 in Dowanol PnB was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of 11 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 324 g of distilled water was stirred into it. Fine adjustment of the viscosity to approx. 2000 mPas afforded a dispersion having the following properties:

Solids content 42.6% by weight Acid value (100%) 18 mg KOH/g OH content (100%, calculated) 2.5% by weight Average particle size 287 nm Viscosity 2030 mPas pH 8.7 The dispersion remained stable at 23° C. for 5 months.

Tests of Coating Properties:

Clearcoats were produced from the preceding examples 1 to 4. (all weights in g):

TABLE 5 Inventive examples 5 to 8 Example 5 6 7 8 1 10.00 2 10.00 3 10.00 4 10.00

The dispersions were homogenized in a SpeedMixer at 2000 rpm for 1 minute applied to a metal coil test plate in a layer thickness of 180 μm (wet) using a coating blade. The plates with the applied wet coatings were for 5 min at room temperature, baked for 30 min at 180° C., and then stored for 24 hours at room temperature. The performance of the stored films was assessed (table 6).

TABLE 6 Tests of the coating properties of the inventive examples 5-8 Example 5 6 7 8 Appearance of the coating (visual examination) clear, glossy clear, glossy clear, glossy silk-matt Film thickness (dry, μ) 60 50 50 40 Pendulum hardness (s) 188 196 189 204 Resistance to xylene (5 minutes) 3 2 3 2 Deionized water (1 hour) 1 0-1 0-1 0-1

As can be seen from table 6, the uretdione-containing dispersions of the invention afford hard and resistant coatings. Both glossy and silk-matt coatings can be produced from the uretdione-containing dispersions of the invention. 

1. An aqueous uretdione group-containing compositions comprising: (A) at least one uretdione group-containing curing agent based on one or more of aliphatic, cycloaliphatic, araliphatic, and aromatic polyisocyanates that contains no chemically-bonded hydrophilizing groups; (B) at least one polyacrylate copolymer; (C) optionally, solvents; and (D) optionally, auxiliaries and additives; wherein the quantitative ratio of the at least one uretdione group-containing curing agent (A) and the at least one polyacrylate copolymer (B) is such that the molar ratio of the NCO groups of the curing agent (A) present as uretdione to NCO-reactive groups of the polyacrylate copolymer (B) is 3.0:0.5 to 0.5:3.0, and wherein (A) and (B) are present as a mixture.
 2. The composition as claimed in claim 1, wherein the at least one uretdione group-containing curing agent (A) was obtained by reacting a monomeric isocyanate comprising at least one monomeric isocyanate selected from the group consisting of tetramethylene diisocyanate, cyclohexane-1,3-diisocyanate and cyclohexane-1,4-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, dicyclohexylmethane-2,4′-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene diisocyanate, triisocyanatononane, toluene diisocyanate, diphenylmethane-2,4′-diisocyanate, diphenylmethane-4,4′-diisocyanate, triphenylmethane-4,4′-diisocyanate, naphthylene-1,5-diisocyanate, and mixtures thereof.
 3. The composition as claimed in claim 1, wherein hydroxyl-containing monomers or polymers are used as starting materials for the at least one uretdione group-containing curing agent (A).
 4. The composition as claimed in claim 1, wherein the at least one uretdione group-containing curing agent (A) has a free NCO content of less than 5% by weight and a content of uretdione groups of 1% to 18% by weight—calculated as C₂N₂O₂, molecular weight 84 g/mol.
 5. The composition as claimed in claim 1, wherein the aqueous composition has an acid value of 1 to 100 mg KOH/g.
 6. The composition as claimed in claim 1, wherein the at least one polyacrylate copolymer is obtained by reacting a mixture of free-radically polymerizable monomers (M), comprising (M1) hydroxyl- and carboxyl-free (meth)acrylic esters having C1 to C12 hydrocarbon radicals in the alcohol moiety; (M2) hydroxyl-functional, free-radically polymerizable monomers; (M3) carboxyl-functional, free-radically polymerizable monomers; (M4) optionally, vinyl esters of aliphatic carboxylic acids; (M5) optionally, at least one cycloaliphatic ester of (meth)acrylic acid and/or vinylaromatics.
 7. The composition as claimed in claim 1, wherein the at least one polyacrylate copolymer (B) has an OH content greater than 1% by weight—calculated as OH groups based on the solids content, molecular weight 17 g/mol—and a number-average molecular weight Mn of 500 to 20 000 g/mol.
 8. The composition as claimed in claim 1, wherein the solvent is selected from the group consisting of acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters, and mixtures thereof.
 9. The composition as claimed in claim 1, wherein the auxiliaries and additives are selected from the group consisting of leveling agents, light stabilizers, catalysts, fillers, and pigments or mixtures thereof.
 10. The composition as claimed in claim 1, wherein the sum of the proportions by weight of (A), (B), and (D) is 30% to 60% by weight based on the solids content of the total aqueous composition.
 11. A process for producing a polyurethane layer comprising the steps of i) providing an aqueous uretdione group-containing composition as claimed in claim 1; ii) applying to a substrate the composition obtained in i) to produce a mixture; iii) drying the mixture from step ii), and iv) curing the mixture from step iii) by heating to from 40° C. to 180° C. for up to 180 minutes.
 12. The process as claimed in claim 11, wherein the aqueous uretdione group-containing composition was obtained by mixing the uretdione group-containing curing agent (A) with the at least one polyacrylate copolymer (B) in the absence of water to form a mixture, and subsequently dispersing the mixture with water.
 13. A polyurethane layer obtained by a process as claimed in claim
 11. 14. A substrate coated or bonded with the polyurethane layer as claimed in claim
 13. 